Speaking of Kasumi I'd say an unpopular opinion I have about her is that whenever she did get a chance to shine her moments really were favorable and noble:
-The Misty Mermaid was a very well-written episode.
-For Cryin' Out Loud tugged at the heart-strings
-Her cameo in AG, especially her interactions with Max and kissing her Pokeball to a Pokemon she once loathed was epic
-Her Chronicle episodes were also decent and realistic because they showed with Misty being on her own, she had to do things her way opposed to Ash's way.
-Her battles with Staryu(although a select few) were just awesome-Movie 3 ring a bell?
My unpopular opinion is that Kasumi did very well had her likeable moments, action-packed moments, and even a few epic moments. She just wasn't given the proper time with the endless amount of fillers to do so.
Just like Iris wasn't given the amount of time saga wise to properly develop her story. I blame the writers for lack of Kasumi utilization in a large span of time and the amount of Iris glorification in such a short span of time.
The writers are at fault for Misty and Iris' developments, not the characters themselves.